Experimental study on frost heave in unsaturated coarse-grained soil caused by vapour transfer

The frost heave caused by vapour transfer has recently attracted much attention, but there is little experimental evidence so far. A series of laboratory experiments are carried out by using the newly developed frost heave apparatus. The results show that considerable frost heave occurs in coarse-grained soil with zero fine content (<0.075 mm) while the specimen is subjected to only vapour supply. The observed frost heave in the 6 cm-high specimen reaches 8.30 mm and 23.46 mm after freezing 336 h and 672 h, respectively. The characteristics of ice lens is observed by the X-TC tests, and the distinct ice lens formation is not observed in the specimen. Under the constant temperature gradient, only one horizontal freezing zone containing segregated ice and saturated pore ice rather than layered ice lens in the frozen soil is observed. The results also show that the frost heave increases with the increasing temperature gradient. Ramped freezing is more conducive to vapour transfer, and leads to greater frost heave than step freezing. A higher initial water content of the soil specimen results in a smaller frost heave in coarse-grained soil. This study has important implications to reveal the mechanism of frost heave in high-speed railways in cold regions.